From: root@mauve.demon.co.uk   
      
   Paul F. Dietz  wrote:   
   > Henry Spencer wrote:   
   >   
   >> The tradeoffs are complex, particularly if you are thinking about using   
   >> extraterrestrial materials (in which case you can forget about the exotic   
   >> advanced cell materials -- you're pretty much restricted to silicon, which   
   >> is not very heat-tolerant).   
   >   
   > That's not entirely clear.  Advanced materials can also be direct bandgap   
   semiconductors,   
   > which absorb light over a much shorter distance than does crystalline   
   silicon.   
   > So, you don't need much actual semiconductor.  What you do need is mundane   
   stuff   
   > like something on which to deposit that material, perhaps a protective glass   
   > cover, wires, heat sinks, and so on.  You could make all that from ET   
   materials   
      
   Also, the actual amount of silicon/... needed may be rather small.   
   Standard solar cells are some .3mm thick, and get 18% or so efficiancy.   
   Assuming that these can be made as cells which can cope with 4* concentration.   
   This is some 800W/m^2.   
   The weight is 600g/m^2, so this is 1333W/Kg.   
   Say $5000/Kg launch costs, so you'r talking about somewhere around $3.75/W.   
      
   Coincidentally, this is about the price (of unconcentrated) solar cells   
   on earth.   
   $7.50 will buy you around 100Kwh on earth.   
      
   If the off-earth resources are free, and the cells last 10 years,   
   it breaks even with current earthly prices.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)